There are various factors in the blur of an image obtained by imaging. For example, there are focus blur which is caused by the deviation of a focusing position during imaging and motion blur which occurs by a camera or a subject moving while a shutter of the camera is opening. Further, when an image is scaled up with pixel interpolation, frequency components higher than the Nyquist frequency disappear, and the blur of the image thereby occurs.
In the present specification, the blur of an image is one aspect of image degradation (the degradation from an original image representing an image that should be obtained by imaging) generated in the process of obtaining the image by imaging (hereinbelow, may also be referred to as “imaging process”), and indicates a phenomenon generated by spread of a group of light beams on an image surface, which should focus (be condensed) on one point.
Conventionally, various techniques have been known as a technique for sharpening a blurred image. For example, there is known a technique in which restoration processing for an attenuated frequency components and generation processing for disappeared frequency components are performed at the same time, and an image obtained by the restoration processing and an image obtained by the generation processing are added.
However, in the generation processing of the above conventional technique, the imaging process (degradation process) is not considered at all. Therefore, the conventional technique does not ensure that an image generated by the generation processing is close to the original image. Therefore, an artifact generated in the generation processing may be mixed into a final result of the addition, and, disadvantageously, an image having an appropriate quality cannot be obtained.